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Re: [TowerTalk] Cutting a FT-240 type 33...in half ??

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Cutting a FT-240 type 33...in half ??
From: Steve Hunt <steve@karinya.net>
Date: Tue, 10 Feb 2015 13:44:55 +0000
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
In the PPT you linked, there are slightly fewer effective turns on the binocular than on the tall stack; he's comparing 3 complete turns through a stack of 8 toroids, with 3 turns through part of the stack and 2 turns through the remainder. You'd expect the relative impedances to be (8*3^2) and (4*3^2+4*2^2) for the tall stack and the binocular respectively; that's an impedance ratio of 1.38:1 which is about what the chart shows consistently at frequencies well below the SRF.

I guess the shift in SRF is then simply down to the difference in inter-winding capacitance between the two arrangements.

Steve G3TXQ



On 10/02/2015 11:35, Ian White wrote:
Interesting question about binocular arrangements of cores (two short stacks of 
cores side by side, vs one tall stack). I found K9YC's comparative measurements 
[1] but am struggling to explain either (a) the shift in resonant frequency or 
(b) the difference in |Z| magnitude.


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